A Framework for Efficient Calculation of Photoionization and Photodetachment Rates With Application to the Lower Ionosphere

• Published in: Journal of geophysical research. Space physics 2020-07, Vol.125 (7), p.n/a
• Main Authors: Janalizadeh, Reza, Pasko, Victor P.
• Format: Article
• Language: English
• Subjects: Ablation; Absorption; Asymmetry; Atmosphere; Atmospheric density; aurora and airglow; Auroras; Earth; Earth ionosphere; Electrons; Ionosphere; Ions; lightning and transient luminous events; Lower ionosphere; metal layers; Negative ions; Nitrogen; Oxygen; Ozone; Photoabsorption; Photodetachment; Photoionization; photoionization and photodetachment; Photons; Radiation absorption; Radiation transport; Scale height; Solar radiation; Transient luminous events; Upper atmosphere; Wavelengths
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2020JA027979

A framework is developed to model photoionization of metals deposited in the lower ionosphere as a result of meteoric ablation and photodetachment of electrons from negative ions of the Earth's ionosphere due to sources of emission other than solar radiation. A wide range of the electromagnetic spectrum including cases of negligible, moderate, and significant absorption of radiation is considered. We limit our scope to the radiation transport through lower ionospheric regions, in case when molecular oxygen, O2, is considered as the main absorber of radiation as photoabsorption due to ozone is only effective at stratospheric altitudes and molecular nitrogen, N2, is transparent to radiation with wavelengths longer than ∼100 nm. We model photon transport in an exponential atmosphere and derive efficient differential representations of the problem in case of negligible photoabsorption and constant pressure approximations. Photoabsorption asymmetry in the atmosphere is demonstrated in case of photons with absorption scales comparable to the scale height of the atmosphere. The application of the model to photoionization in the lower ionosphere is demonstrated by considering photoionization of meteoric species due to photons of the Lyman‐Birge‐Hopfield (LBH) band system of N2 observed in the aurora and in the lightning‐induced transient luminous events. Furthermore, we model detachment of electrons from negative ions of the ionosphere due to the first positive and the second positive band systems of N2, and the first negative band system of N 2+, also observed in the sources mentioned above. Plain Language Summary We provide a framework to calculate rates of photoionization and photodetachment in the lower ionosphere due to sources other than solar radiation while accounting for photoabsorption in the upper atmosphere of the Earth with exponential variation of air density with altitude. The photoionization (or photodetachment) problem is presented in an integral form and subsequently converted to an equivalent differential form in case of negligible photoabsorption and constant pressure media in order to obtain a solution in a time‐efficient manner. The asymmetric photoabsorption in the atmosphere is demonstrated in cases where the above approximations are not valid, that is, for photons with absorption scales comparable to the scale height of the atmosphere. As applications of the framework we consider photoionization of metals constituting the metal layers in E